U.S. patent number 4,479,856 [Application Number 06/521,373] was granted by the patent office on 1984-10-30 for zinc dendrite inhibitor.
This patent grant is currently assigned to Meidensha Electric Mfg. Co., Ltd.. Invention is credited to Yasuo Ando.
United States Patent |
4,479,856 |
Ando |
October 30, 1984 |
Zinc dendrite inhibitor
Abstract
A dendrite inhibitor includes a quaternary ammonium salt and at
least two metal ions selected from the group consisting of lead,
tin and cadmium ions, and the inhibitor is used by adding it to an
electrolyte for subjecting zinc to electrolysis through an
electrochemical reaction.
Inventors: |
Ando; Yasuo (Mitaka,
JP) |
Assignee: |
Meidensha Electric Mfg. Co.,
Ltd. (Tokyo, JP)
|
Family
ID: |
15196787 |
Appl.
No.: |
06/521,373 |
Filed: |
August 8, 1983 |
Foreign Application Priority Data
|
|
|
|
|
Aug 9, 1982 [JP] |
|
|
56-137358 |
|
Current U.S.
Class: |
205/312; 205/313;
429/201 |
Current CPC
Class: |
H01M
10/02 (20130101); C25D 3/22 (20130101); H01M
10/365 (20130101); Y02E 60/10 (20130101) |
Current International
Class: |
C25D
3/02 (20060101); C25D 3/22 (20060101); H01M
10/02 (20060101); H01M 10/36 (20060101); C25D
003/22 () |
Field of
Search: |
;204/55R,DIG.2
;429/199,201 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Andrews; R. L.
Attorney, Agent or Firm: Fleit, Jacobson, Cohn &
Price
Claims
What is claimed is:
1. A zinc dendrite inhibitor for addition to a zinc
halide-containing electrolyte which deposits zinc on a negative
electrode through an electrochemical reaction, said inhibitor
comprising: a quaternary ammonium salt and at least two metal ions
selected from the group consisting of from about 10.sup.-4 to about
10.sup.-3 mole/l of divalent lead ions, from about 10.sup.-4 to
about 10.sup.-3 mole/l of divalent tin ions, and less than about
10.sup.-2 mole/l of divalent cadmium ions.
2. An inhibitor according to claim 1, wherein said quaternary
ammonium salt comprises a chemical compound having the general
formula R.sub.1 R.sub.2 R.sub.3 R.sub.4 N.sup.+ X.sup.-, where
R.sub.1, R.sub.2, R.sub.3 and R.sub.4 are radicals selected from
the group consisting of alkyl and benzyl radicals, wherein at least
2 of R.sub.1, R.sub.2, R.sub.3 and R.sub.4 are alkyl radicals each
having a carbon number of at most 12, and where X is a radical
selected from the group consisting of halogen, 1/2 SO.sub.4, and
morpholine.
3. An inhibitor according to claim 1, wherein said metal ions are
presented by donors selected from the group consisting of halides,
sulfates, acetates and phosphates.
4. An inhibitor according to claim 1, wherein said quaternary
ammonium salt has a concentration ranging from 10.sup.-4 mole/l to
the saturated concentration thereof.
5. An inhibitor according to claim 1, wherein the concentration of
said lead ions and said tin ions is each 5.times.10.sup.-4 mole/l
and wherein the concentration of said cadmium ions is in the range
of from about 10.sup.-4 to about 10.sup.-3 mole/l.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a zinc dendrite inhibitor whereby
in an electrolyte circulation-type secondary cell using zinc as an
active material or in the case of electrochemical zinc plating, the
zinc deposited and grown on an electrode surface is prevented from
developing into dendritic crystals (hereinafter referred to as
dendrites) and a smooth deposited zinc surface is produced.
2. Description of the Prior Art
The electrolyte circulation-type secondary cell is basically
constructed as shown in FIG. 1 and it uses zinc
halide-electrolytes. This cell comprises a unit cell 1 partitioned
by a separating membrane (separator) 2 to form a positive electrode
chamber 3 and a negative electrode chamber 4 on its sides, a
positive electrode 5 positioned in the positive electrode chamber 3
and a negative electrode (zinc electrode) 6 positioned in the
negative electrode chamber 4. A positive electrode electrolyte
(e.g., ZnBr.sub.2 +Br.sub.2) is circulated through the positive
electrode chamber 3 from a positive electrode electrolyte storage
tank 7 by a pump 9 and a negative electrode electrolyte (e.g.,
ZnBr.sub.2) is circulated through the negative electrode chamber 4
from a negative electrolyte storage tank 8 by a pump 13. Numerals
11 and 12 designate valves which are opened during the charging and
discharging, respectively.
When the above-mentioned cell is charged, bromine is deposited on
the positive electrode side indicated by .sym. and zinc is
deposited on the negative electrode side indicated by .crclbar..
While there is no problem if the deposited zinc forms uniformly and
gradually increases its thickness on the negative electrode
surface, generally the deposited zinc tends to develop into
dendrites and grows locally due to various causes.
The process of formation of dendrites on the negative electrode
surface is considered to approximately include the following steps.
In other words, during the initial charging period metal zinc
deposited on the negative electrode surface does not necessarily
grow uniformly over the whole surface of the electrode but the
metal zinc is deposited in a spotty manner. During this period,
what can be considered as nuclei of dendrites are already produced.
As a result, if the charging and discharging are continued in such
a condition, the electrodeposition preferentially takes place at
the spottily produced nuclei thus eventually producing
dendrites.
When the dendrites grow on the negative electrode surface, the
electric field concentrates so that the rate of growth of the
dendrites increases and the chance of the zinc electrode surface
contacting a fresh supply of the electrolyte decreases, thus not
only deteriorating the cell efficiency but also causing the
extremely fragile dendrites to fall off the electrode by a
relatively small stress. As a result, the dendrites fallen off in
this way cause clogging of the electrolyte circulation pipe and
deterioration of the pump efficiency.
Assuming that such dendrites do not fall off the electrode but
continue to grow so that the dendrites continue to grow
progressively as shown at a, b and c in FIG. 2 or the growth
progresses extremely, the dendrites directly contact with the
positive electrode surface so that a electric short-circuit is
formed and eventually the cell is damaged. Thus, the inhibition of
growth of dendrites constitutes one of the very important
requirements.
Such undesired phenomena occur even in the case of a
electrochemical plating involving the electrolysis of zinc giving
rise to a disadvantage of damaging the smoothness of a processed
object.
In view of these requirements, various studies have been made on
dendrite inhibitors and ionic or nonionic surface active agents,
zinc electrochemical plating brighteners, etc., have for example
been used. However, these agents are inadequate and leave much room
for improvement with respect to such chemical resistances as
resistance to bromine, the smoothness of deposited zinc with a
large current density and large electrical quantity and so on.
Also, these agents are not capable of maintaining stable
performance during cyclic use over a long period of time and they
are also inadequate in terms of the essential dendrite inhibitory
effect.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an inhibitor
capable of effectively inhibiting the deposition of dendrites.
In accordance with the invention there is thus provided a dendrite
inhibitor including a quaternary ammonium salt and one or more
metal ions selected from the group consisting of lead, tin and
cadmium ions and used by mixing with an electrolyte for effecting
the electrolysis of zinc by an electrochemical reaction.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The quaternary ammonium salt used with the present invention may
consist of a chemical compound having the general formula [R.sub.1
R.sub.2 R.sub.3 R.sub.4 N].sup.+ X.sup.- (where R.sub.1, R.sub.2,
R.sub.3 and R.sub.4 are radicals such as alkyl, benzyl or phenyl
radicals and X represents a halogen, 1/2 SO.sub.4 or an
intermolecular quaternary ammonium salt formed by one or more
heterocyclic compounds selected from the group consisting of
morpholine, piperidine and pyrolidine. More specifically,
trimethyldodecylammonium, dimethylbenzyldodecylammonium,
trimethylphenylammonium, methylethylmorpholinium,
methylethylpiperidinium, methylethylpyrolidinium, etc., may for
example be used.
On the other hand, lead, tin or cadmium ions are provided in the
form of halides, sulfates, acetates, phosphates or the like and the
resulting negative ions, have no effect on the electrochemical
reaction.
The following Table 1 shows the results of tests conducted by
adding varying amounts of lead, tin and cadmium ions to zinc
electrolytes containing quaternary ammonium salts and examining the
resulting dendrite inhibitory effects. The addition of the metal
ions was effected by adding SnCl.sub.2, PbBr.sub.2 and
CdBr.sub.2.
Under the testing conditions of zinc bromide 3 mole/l pH 2.5 and
charging current density 40 mA/cm.sup.2, the conditions obtained
after the charging for 8 hours were observed.
TABLE 1
__________________________________________________________________________
Added amounts, mole/l Quaternary Ammonium Evalua- Pb.sup.++
Sn.sup.++ Cd.sup.++ Salt, mole/l tion Others
__________________________________________________________________________
0 0 0 0 D Large quantity of dendrites, electric shorting during
charging 5 .times. 10.sup.-4 0 0 0 C Large quantity of small
dendrites 0 5 .times. 10.sup.-4 0 0 C 0 0 5 .times. 10.sup.-4 0 C 0
0 0 Methylethylmorpholiniumbromide, 1 C 0 0 0
Methylethylmorpholiniumbromide, 1, B Practically no dendrite,
dimethylbenzyldodecylammonium some surface irregularities, bromide,
1 .times. 10.sup.-4 no luster 5 .times. 10.sup.-4 0 0
Methylethylmorpholiniumbromide, 1 C 0 5 .times. 10.sup.-4 0 " C 0 0
5 .times. 10.sup.-4 " C 5 .times. 10.sup.-4 5 .times. 10.sup.-4 0 "
A Smooth with no luster 5 .times. 10.sup. -4 0 5 .times. 10.sup.-4
" B 0 5 .times. 10.sup.-4 5 .times. 14.sup.-4 " B 0 0 0
Tetrabuytlammonium bromide, 0.01 B 0 0 0 Trimethyldodecylammonium,
bromide B 0.01 10.sup.-4 10.sup.-4 10.sup.-4
Methylethylmorpholiniumbromide, 1 A Smooth surface 2 .times.
10.sup.-4 2 .times. 10.sup.-4 2 .times. 10.sup.-4 " A Smooth
surface 5 .times. 10.sup.-4 5 .times. 10.sup.-4 5 .times. 10.sup.-4
" A Smooth surface with metallic luster 7.5 .times. 10.sup.-4 7.5
.times. 10.sup.-4 7.5 .times. 10.sup.-4 " A Smooth surface with
metallic luster 10.sup.-3 10.sup.-3 10.sup.-3 " A Whitish
electrolyte, smooth surface 5 .times. 10.sup.-4 5 .times. 10.sup.-4
5 .times. 10.sup.-4 Tetrabutylammonium bromide, 0.01 A Metallic
luster " " " Trimethyldodecylammonium bromide, A " 0.01 " " "
Dimethylbenzyldodecylammonium A " bromide, 10.sup.-4 " " " 0 B
10.sup.-3 10.sup.-3 10.sup.-3 0 B
__________________________________________________________________________
The evaluation A indicates a smooth surface without any dendrite,
the evaluation B a surface having irregularities, the evaluation C
a surface having a large quantity of small dendrites and the
evaluation D a surface having a large quantity of dendrites.
These results have shown that by adding to an electrolyte a
quaternary ammonium salt mixed with a suitable amount of lead, tin
or cadmium ions, it is possible to inhibit the deposition of
dendrites effectively and produce a deposited zinc surface which is
smooth and has a metallic luster.
Further, the 6-hour charging and discharging cycle tests at 40
mA/cm.sup.2 have shown at the tests of over 20 cycles with the
addition of 5.times.10.sup.-4 mole/l of lead, tin and cadmium ions,
respectively, resulted in deposited zinc surfaces which were smooth
and having a metallic luster.
With the addition of no lead, tin or cadmium, the first cycle
showed the deposition of small dendrites and the third cycle showed
the occurrence of electric short-circuiting between the positive
electrode and the negative electrode due to the falling off of the
dendrites from the electrode, etc. This result also shows that the
addition of lead, tin or cadmium is especially effective in the
case of secondary battery.
Then, using the electrolytes containing 5.times.10.sup.-4 mole/l of
lead, tine and cadmium ions, respectively, and 1 mole/l of
methylethylmorpholiniumbromide and varying the current density, the
resulting dendrite inhibitory effects were examined and the
following results were obtained. The charging electric quantity
used was 240 mA.H/cm.sup.2.
TABLE 2 ______________________________________ Current density
(mA/cm.sup.2) Evaluation ______________________________________ 20
A 40 A 60 A 80 A 100 B ______________________________________
From these test results it has been confirmed that satisfactory
inhibition of dendrites is ensured even at high current
densities.
Then, in addition to the examinations shown in Table 1, the
extensive examinations were made on the concentration of the
quaternary ammonium salts and the metal ions added and used with
the former and it has been confirmed that the desired effects due
to their use could be displayed if the quaternary ammonium salt
concentration is in the range from over 10.sup.-4 mol/l to the
saturated concentration, the additional lead ion concentration is
in the range from 1.times.10.sup.-4 to the saturated concentration,
preferably 5.times.10.sup.-4 mole/l, the additional tin ion
concentration is substantially in the same range as the former and
the cadmium ion concentration is in the range from 0 to 10.sup.-2
mole/l, preferably in the range from 1.times.10.sup.-4 to
1.times.10.sup.-3 mole/l.
From the foregoing description it will be seen that the use of an
inhibitor according to the invention has the effect of effectively
suppressing the deposition of dendrites even at high current
densities and producing a deposited zinc surface which is smooth
and having a metallic luster. Further, this inhibitor contains
metal ions and a quaternary ammonium salt and therefore it has no
danger of decomposition, etc.
* * * * *